Industrial pressure sensitive switches are used in hydraulic control systems, particularly hydraulic control systems for machine tools. Such pressure sensitive switches must meet a number of demanding criteria. The pressure sensitive switches must be capable of operating at their "trip pressure" in an accurate manner. That is, each time the switch operates it should operate at substantially the same "trip pressure". Also, industrial pressure sensitive switches may be subjected to large pressure transients in the hydraulic system. A large pressure transient may occur in the situation where a pressure reservoir is maintained at high pressure and a hydraulic valve is opened to that pressure reservoir very rapidly, as for example, by a solenoid. An example of an industrial pressure switch is shown in Edwards, Jr. et al., U.S. Pat. No. 4,168,415, issued Sept. 18, 1979.
The pressure sensitive switch shown in the Edwards, Jr. et al. reference provides a good general purpose industrial type hydraulic pressure switch. However, when accuracy of the "trip pressure" requirements and requirements for sustaining high rate of rise pressure transients in the hydraulic system exceed the design envelope of the apparatus shown in the Edwards. Jr. et al. reference, the pressure sensitive switch shown in the reference may be unsuitable. Particularly, pressure transients of the order of 1,500 psi/millisecond may occur within modern industrial hydraulic systems, and such transients are outside of the design envelope of the switch shown in the Edwards, Jr. et al. reference. Also, it is desirable to reduce the friction experienced by the piston actuator disclosed in the Edwards, Jr. et al. reference.